Article pubs.acs.org/IC
Reactivity of a Tin(II) (Iminophosphinoyl)(thiophosphinoyl)methanediide Complex Toward Sulfur: Synthesis and 119Sn Mössbauer Spectroscopic Studies of [{( μ-S)SnC(PPh2NSiMe3) (PPh2S)}3Sn( μ3-S)] Jia-Yi Guo,† Hong-Wei Xi,§ Israel Nowik,‡ Rolfe H. Herber,*,‡ Yongxin Li,† Kok Hwa Lim,§ and Cheuk-Wai So*,† †
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore ‡ Racah Institute of Physics, The Hebrew University of Jerusalem, Kaplun 23, 91904 Jerusalem, Israel § Division of Chemical and Biomolecular Engineering, School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, 637459 Singapore S Supporting Information *
ABSTRACT: Reaction of [(PPh2NSiMe3)(PPh2S)CSn:]2 (1) with elemental sulfur in toluene afforded [{(μ-S) SnIVC(PPh2NSiMe3)(PPh2S)}3SnII(μ3-S)] (2) and [CH2(PPh2NSiMe3)(PPh2S)] (3). Compound 2 comprises a SnIIS moiety coordinated with the SnIV and S atoms of a trimeric 2-stannathiomethendiide {(PPh2NSiMe3)(PPh2S)CSn(μ-S)}3. Compound 2 has been characterized by NMR spectroscopy, 119Sn Mössbauer studies, X-ray crystallography, and theoretical studies. 119Sn NMR spectroscopy and Mössbauer studies show the presence of SnIV and SnII atoms in 2. X-ray crystallography suggests that the SnIIS moiety does not have multiple bond character. Theoretical studies illustrate that the Cmethanediide−Sn bonds comprise a lone pair orbital on each Cmethanediide atom and an C−Sn occupied σ orbital.
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INTRODUCTION Tin(II) sulfide (SnS) occurs naturally as herzenbergite. At room temperature, it adopts a distorted rock-salt layered structure. Each tin atom in herzenbergite forms three short Sn− S bonds (2.7 Å) within the layer and three long Sn−S bonds (3.4 Å) connecting two neighboring SnS layers.1 Moreover, there is a lone pair of electrons (5s2) at each tin atom. Since SnS has a narrow band gap of 1.3 eV, its thin films and nanocrystals have been synthesized and investigated extensively as holographic recording systems, solar control devices, and photovoltaic materials.2 In contrast, a stable monomeric tin(II) sulfide molecule, which is the heavier analogue of carbon monoxide, is still unknown. Recently, several research groups demonstrated that reactive species can be stabilized by forming an adduct with both Lewis acid and Lewis base.3 For example, Rivard et al. reported that the heavier ethylene analogues [IPr → Si(H2)E(H2) → W(CO)5] (IPr = {HCN(2,6-Pri2C6H3)}2C:, © 2012 American Chemical Society
E = Ge or Sn) are stabilized by a N-heterocyclic carbene (Lewis base) and W(CO)5 (Lewis acid).3a Moreover, Hahn et al. showed that a SnO moiety can be trapped by a lutidene-bridged bisstannylene during reaction of the bistannylene with water.3g We anticipate that a monomeric tin(II) sulfide moiety could be isolable by coordinating the tin and sulfur atoms with suitable Lewis acid and base. Recently, we reported the synthesis and characterization of a tin(II) methanediide complex [(PPh 2NSiMe 3)(PPh2S)CSn:]2 (1).4 X-ray crystallography and DFT calculations suggest that the Sn−C bond in compound 1 has a >CSn: skeleton, which is stabilized by the lone pair of electrons on the nitrogen and sulfur donors. In this paper, we describe the reaction of 1 with elemental sulfur to form Received: September 7, 2011 Published: March 12, 2012 3996
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state at room temperature under an inert atmosphere. Orange crystals of 2 are soluble in CH2Cl2 only, and it decomposes slowly in solution to give 3. Compound 2 can be considered as an intermediate during decomposition of the unstable 2-stannathiomethendiide intermediate “(PPh2NSiMe3)(PPh2S)CSnS”. Thus, when the reaction of 1 with elemental sulfur in toluene was performed overnight, only compound 3 formed. A freshly prepared solution of 2 in CD2Cl2 was characterized by NMR spectroscopy. The 1H NMR spectrum shows one singlet (δ −0.29 ppm) and multiplets (δ 6.88−7.38 ppm) for the SiMe3 and phenyl protons, respectively. In the molecular structure of 2 (Figure 3), the S(1−3) atoms have similar orientation toward the Sn(4) atom but the Sn(4)−S(2−3) bond lengths are shorter than the Sn(4)···S(1) distance. These lead to nonequivalent P(2,4,6) atoms. However, the 31P{1H} NMR spectrum at room temperature or −60 °C shows two doublets at δ 27.42 and 30.07 ppm, which correspond to two nonequivalent phosphorus nuclei. The results are not consistent with the solid-state structure. These indicate that the thiophosphinoyl substituents are fluxional in solution or the S(1−3) atoms may be equivalent in solution with equal Sn(4)···S(1−3) distances. The 119Sn{1H} NMR spectrum of 2 at room temperature or −60 °C shows a multiplet at δ −242.1 ppm. 119 Sn solid-state NMR spectroscopy was performed. The 119Sn CPMAS NMR signals (δiso = −260.3 (Sn(4)), −232.3 ppm (Sn(1−3)) show two nonequivalent tin environments in 2. The isotropic chemical shift for the Sn(1−3) atoms (δiso = −232.3 ppm) shows an upfield shift compared with the 119Sn NMR signal of [Sn{N(SiMe3)2}2(μ-S)]2 (δ −106.6 ppm).7 The isotropic chemical shift for the Sn(4) atom (δiso = −260.3 ppm) shows an upfield shift compared with the 119Sn NMR signal of SnO trapped by the lutidene-bridged bisstannylene (δ −85.1 ppm).3g Temperature-Dependent 119Sn Mössbauer (ME) Studies. ME spectra of 2 were examined over the range 5.5 < T < 181 K and give evidence of three distinct tin sites. As usual, these resonances consist of well-resolved doublets, and a typical spectrum at 91.7 K is shown in Figure 1. As will be noted the
[{(μ-S)SnIVC(PPh2NSiMe3)(PPh2S)}3SnII(μ3-S)] (2). Compound 2 comprises a SnIIS moiety coordinated with the SnIV and S atoms of a trimeric 2-stannathiomethendiide {(PPh2NSiMe3)(PPh2S)CSn(μ-S)}3. 119Sn Mö ssbauer spectroscopic studies of 2 were also performed to identify the oxidation states of tin atoms. For clarity, the tin(IV) atoms of 2 are labeled as Sn(1), Sn(2), and Sn(3), while the tin(II) atom is labeled as Sn(4).
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RESULTS AND DISCUSSION
Synthesis of [{(μ-S)Sn IV C(PPh 2 NSiMe 3 )(PPh 2
S)}3SnII(μ3-S)] (2). Reaction of 1 with elemental sulfur in toluene for 4 h afforded a mixture of [{(μ-S)SnIVC(PPh2 NSiMe3)(PPh2S)}3SnII(μ3-S)] (2), [CH2(PPh2NSiMe3)(PPh2S)] (3),5 and unidentified minor products, which was confirmed by NMR spectroscopy (Scheme 1). Pure compound Scheme 1. Synthesis of 2 and 3
2 can be isolated as orange crystals in 29.2% yield by recrystallization in toluene. The reaction appears to proceed through an oxidative addition of 1 with elemental sulfur to form an unstable 2-stannathiomethendiide intermediate “(PPh2 NSiMe3)(PPh2S)CSnS”, which then decomposes to form intermediates “(PPh2NSiMe3)(PPh2S)C:” and “SnS”. A monomeric SnS moiety is trapped by the SnIV and S atoms of a trimeric 2-stannathiomethendiide {(PPh2NSiMe3)(PPh2 S)CSn(μ-S)}3 to form 2. Subsequently, 3 could be formed by hydrogen abstraction of “(PPh2NSiMe3)(PPh2S)C:” with the solvents. Chivers et al. reported that the intermediate [:C(PPh2S)2] dimerizes to form [(SPh2P)2C2(PPh2)2S2], which contains a six-membered C2P2S2 ring.6 However, dimerization of “(PPh2NSiMe3)(PPh2S)C:” cannot be observed in the reaction of 1 with elemental sulfur in toluene; instead, compound 3 was formed. Moreover, when the reaction of 1 with elemental sulfur was performed in THF for 20 min, a mixture of 2 and 3 can be isolated in a ratio of 1:1, which was confirmed by NMR spectroscopy. The results illustrate that decomposition of “(PPh2NSiMe3)(PPh2S)CSnS” and hydrogen abstraction of “(PPh2NSiMe3)(PPh2S)C:” are enhanced in a polar solvent. Compound 2 is stable in the solid
Figure 1.
119
Sn Mössbauer spectrum of compound 2 at 91.7 K.
spectrum consists of a major resonance at an isomer shift (IS) of about 1.17 mm s−1, a second absorbance at an IS of about 3.56 mm s−1, and a third site at an IS of about 2.2 mm s−1, all with respect to the room-temperature BaSnO3 reference point. The major site is clearly due to Sn(IV), while the second resonance arises from a Sn(II) site. The hyperfine interaction 3997
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X and M subscripts indicate the X-ray- and ME-derived values, respectively. Again, the msav data for the Sn(4) atom indicate a significantly larger value than those for the Sn(1−3) atoms, consistent with the dynamical data referred to above. As noted previously for 119Sn data,9 the F̵ values derived from the ME data are consistently smaller than those derived from the X-ray values, and the differences are presumed to arise from the presence of crystal lattice imperfections and/or the presence of low-lying librational and torsional motions of the metal atom, which are slow on the ME time scale but cumulatively averaged in the X-ray data. Again, these observations are consistent with a softer metal atom−S ligation in the case of the Sn(4) atom than in the case of the Sn(1−3) atoms as indicated above. X-ray Crystal Structure of 2. Single crystals suitable for X-ray crystallography were obtained by recrystallization of 2 in C6D6. The molecular structure of 2 is shown in Figure 3. Phenyl substituents and disordered solvent molecules are omitted for clarity in the figure. The numbering scheme of tin atoms in the molecular structure is same as in Scheme 1. Selected bond lengths and angles of 2 are shown in Table 2.
parameters (IS and QS) of these two sites at 91.7 K are summarized in Table 1. These hyperfine parameters are unfortunately Table 1. 119Sn Mössbauer Spectroscopic Data of 2 at 91.7 Ka atom
IS
QS
Γ
formal oxidation state
IR
Sn(4) Sn(1−3)
3.57(3) 1.170(4)
0.87(2) 1.550(4)
0.84(7) 0.87(1)
+II +IV
0.203 1.00
IS: isomer shift (mm s−1). QS: electric quadrupole splitting (mm s−1). Γ: experimental line width (mm s−1). IR: relative intensity.
a
not sufficiently temperature sensitive to permit a meaningful calculation of the effective mass and ME lattice temperature, since the recoil-free fraction, f, becomes very small above about 200 K. The chemical identity of the third resonance (amounting to about 4% of the total area at 91.7 K) cannot be identified from the present data. However, the temperature dependence of the f parameter, which is given by the temperature dependence of the area under the resonance curve for an optically thin absorber, is determinable. For the Sn(1−3) atoms, (−d ln A)/ dT = 20.5(2) × 10−3 with a correlation coefficient of 0.986 for 10 data points. For the Sn(4) atom, (−d ln A)/dT = 24.9(2) × 10−3 with a correlation coefficient of 0.96 for 10 data points. These data are summarized graphically in Figure 2 in terms of
Table 2. Selected Bond Lengths (Angstroms) and Angles (degrees) of Compound 2
Figure 2. Temperature dependence of the F parameter for the Sn(1−3) atoms (○) and the Sn(4) atom (●) of 2.
the parameter F̵ = k2⟨xave2⟩, vide infra, from which it is clear that the Sn(II) site is significantly softer than the Sn(IV) sites. This observation is also consistent with the temperature dependence of the area ratio of the two sites, R = ASn(4)/ ASn(1−3) which decreases with increasing temperature due to the difference in the temperature dependence of the recoil-free fractions as referred to above. To focus on the metal atom dynamics in 2, the Ui,j values extracted from the single-crystal X-ray data (see the Supporting Information) have been used to evaluate the mean square amplitude of vibration (msav) of the Sn atoms and compare this to the value extracted from the temperature-dependent ME data, as described previously.8 The msav is best expressed in terms of the F parameter, where F̵ = k2⟨xave2⟩ and k2 is the square of the ME gamma-ray wave vector (1.464 × 1018 cm2). The values so calculated are F̵X,103 = 2.78 ± 0.12 for the Sn(1−3) atoms and F̵M,103 = 2.11 ± 0.21. For the Sn(4) atom, F̵ X,103 = 3.66 ± 0.12 and F̵M,103 = 2.57 ± 0.26, all at 103 K, where the
Sn(4)−S(7) Sn(4)−S(3) Sn(2)−S(7) Sn(1)−S(4) Sn(2)−S(4) Sn(3)−S(5) C(1)−Sn(1) C(1)−P(2) P(2)−S(1) C(29)−Sn(2) C(29)−P(4) P(4)−S(2) C(57)−Sn(3) C(57)−P(6) P(6)−S(3) Sn(4)···S(1) S(2)−Sn(4)−S(3) S(3)−Sn(4)−S(7)
2.6119(19) 2.813(3) 2.678(2) 2.407(2) 2.412(2) 2.415(2) 2.104(8) 1.698(8) 2.015(3) 2.119(7) 1.701(8) 2.031(3) 2.119(8) 1.697(8) 2.011(3) 2.920(2) 106.75(8) 88.51(7)
Sn(4)−S(7)− Sn(2) S(4)−Sn(1)−S(5)
129.63(8) 114.63(8)
S(5)−Sn(3)−S(6)
113.49(7)
S(6)−Sn(2)−S(4)
111.41(7)
P(1)−C(1)−P(2) P(2)−C(1)−Sn(1) P(3)−C(29)− Sn(2) P(5)−C(57)−P(6)
136.6(5) 128.8(4) 93.8(3)
P(6)−C(57)− Sn(3)
134.7(5)
Sn(4)−S(2) Sn(1)−S(7) Sn(3)−S(7) Sn(1)−S(5) Sn(2)−S(6) Sn(3)−S(6) C(1)−P(1) P(1)−N(1) N(1)−Sn(1) C(29)−P(3) P(3)−N(2) N(2)−Sn(2) C(57)−P(5) P(5)−N(3) N(3)−Sn(3) S(2)−Sn(4)−S(7) Sn(4)−S(7)− Sn(1) Sn(4)−S(7)− Sn(3) Sn(1)−S(5)− Sn(3) Sn(3)−S(6)− Sn(2) Sn(2)−S(4)− Sn(1) P(1)−C(1)−Sn(1) P(3)−C(29)−P(4) P(4)−C(29)− Sn(2) P(5)−C(57)− Sn(3)
2.686(3) 2.6771(19) 2.659(2) 2.410(2) 2.404(2) 2.412(2) 1.717(8) 1.612(7) 2.223(6) 1.722(8) 1.620(7) 2.217(7) 1.722(8) 1.606(7) 2.250(7) 88.53(7) 127.97(8) 129.95(8) 96.34(7) 95.66(7) 96.49(7) 94.3(3) 133.3(5) 130.1(4) 93.8(4)
130.3(5)
The methanediide ligands are coordinated in a C,N-chelate fashion to the Sn(1), Sn(2), and Sn(3) atoms, which adopt a distorted trigonal bipyramidal geometry. The C(1)−Sn(1) (2.104(8) Å), C(29)−Sn(2) (2.119(7) Å), and C(57)−Sn(3) (2.119(8) Å) bonds are shorter than that in 1 (2.199(4) Å) and 3998
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the 1,3-distannacyclobutane [Sn{μ2-C(PPh2NSiMe3)2}]2 (average 2.322 Å).10 The Sn(1)−N(1) (2.223(6) Å), Sn(2)− N(2) (2.217(7) Å), and Sn(3)−N(3) (2.250(7) Å) bonds in 2 are comparable with that in 1 (2.2554(8) Å). Moreover, they are longer than the terminal Sn−N σ bond in [:Sn{N(SiMe3)2}2] (2.088(6), 2.096(1) Å).11 The S(4), S(5), and S(6) atoms are bridged between the Sn(1), Sn(2), and Sn(3) atoms. The Sn−S(4), Sn−S(5), and Sn−S(6) bonds (2.404(2)−2.415(2) Å) are comparable with the Sn−S single bonds in [(Tbt)(Mes)Sn(μ-S)] 2 (Tbt = 2,4,6-{CH(SiMe3)2}3C6H2, 2.434(3) and 2.432(3) Å)12 and [Sn{N(SiMe3)2}2(μ-S)]2 (2.416(5) and 2.413(6) Å).7 In addition, the S(1−3) atoms of the thiophosphinoyl substituents have a similar orientation toward the Sn(4) atom. It is noteworthy that the S(1)···Sn(4) distance (2.920(2) Å) is significantly longer than the S(2)−Sn(4) (2.686(3) Å) and S(3)−Sn(4) bond lengths (2.813(3) Å), but the S(1)···Sn(4) distance is shorter than the sum of van der Waals’ radii (ca. 4 Å). This suggests that there is a weak interaction between the S(1) and the Sn(4) atoms. The S(7)−Sn(4)−S(2) and S(7)−Sn(4)−S(3) angles are almost 90°, which imply that the Sn(4) atom possesses high-s-character lone pairs (see below). The Sn(4)−S(7) bond (2.6119(19) Å) is significantly longer than the Sn−S single bonds in [(Tbt)(Mes)Sn(μ-S)]2 (2.434(3) and 2.432(3) Å)12 and [Sn{N(SiMe3)2}2(μ-S)]2 (2.416(5) and 2.413(6) Å),7 which indicates that there is no multiple-bond character between the Sn(4) and the S(7) atoms (see below). Furthermore, the geometry around the S(7) atom is tetrahedral. These imply that there are three lone pairs of electrons on the S(7) atom for formation of the S(7)−Sn(1−3) bonds (2.659(2)− 2.678(2) Å). Theoretical Studies of 2. In order to understand the bonding nature in compound 2, it was investigated by DFT calculations.13 The optimized geometry of 2 (B3PW91/ LANL08d for Sn, 6-31+G(d) for Cmethanediide, N, P, S and Si, 6-31G(d) for C and H level) is in good agreement with the X-ray crystallographic data except the Sn(4)···S(1) distance and S(2)−Sn(4)−S(3) angle (Figure S1 with selected bond lengths and angles, see the Supporting Information). It is proposed that the crystal packing force leads to a stronger Sn(4)···S(1) interaction and hence a smaller S(2)−Sn(4)−S(3) angle in the X-ray crystal structure of 2 (Figure 3). The natural bond orbital (NBO) analysis (Table S1, see the Supporting Information)14 of 2 shows that there is a lone pair of electrons at the Sn(4) atom. The percentage of the s character of the lone pair orbital is high (93.5%). The Sn(4)−S(7) bond comprises an occupied σ orbital (electron occupancy = 1.98) only. It is formed by the overlapping of a sp21.93 hybrid with 95.3% p character on the Sn(4) atom and a sp1.85 hybrid on the S(7) atom. The results indicate that there is no multiplebond character between the Sn(4) and the S(7) atoms. Moreover, the Sn(4)−S(2) bond is formed by the overlapping of a sp59.07 hybrid with 97.85% p character on the Sn(4) atom and a sp5.69 hybrid on the S(2) atom. The Sn(4)−S(3) bond is formed by the overlapping of a p orbital on the Sn(4) atom and a sp5.99 hybrid on the S(3) atom. The results are consistent with the X-ray crystallographic data that the S(7)−Sn(4)−S(2) and S(7)−Sn(4)−S(3) angles are almost 90°. In addition, NBO analysis shows that the Cmethanediide−Sn bonds (C(1)−Sn(1), C(29)−Sn(2), C(57)−Sn(3)) comprise a lone pair orbital (LP) on each Cmethanediide atom and an C−Sn occupied σ orbital. The LP(C(1)), LP(C(29)), and LP(C(57)) are p orbitals which are stabilized by forming p−σ* negative
Figure 3. Molecular structure of 2 with thermal ellipsoids at the 20% probability level. Phenyl substituents, disordered solvent molecules, and hydrogen atoms are omitted for clarity.
hyperconjugation with the σ*(P−C), σ*(P−S), and σ*(Sn−S) orbitals (stabilizing energy = 61.16 kcal mol−1 for LP(C(1)), 60.52 kcal mol−1 for LP(C(29)), and 60.03 kcal mol−1 for LP(C(57)), Table S3, Supporting Information). The Sn(1)− C(1), Sn(2)−C(29), and Sn(3)−C(57) bonds are highly polarized toward the Cmethanediide atoms (Sn(1)−C(1) bond = 81.3%, Sn(2)−C(29) = 81.9%, Sn(3)−C(57) = 81.6% polarization). Moreover, the NPA charges (Table S2, Supporting Information) of the Cmethanediide (−1.71 to −1.73) and Sn(1−3) atoms (1.89−1.90) indicate that the bonding between the Cmethanediide atoms and the tin(IV) atoms is highly ionic. Furthermore, NBO analysis shows that the P−C, P−S, and P−N bonds are single bonds (Wiberg bond index (WBI)15 of P−C, 1.02−1.06; P−N, 0.95; P−S, 1.08−1.18). Together with the NPA charges of the Cmethanediide, P(1−6), N(1−3), and S(1−3) atoms (Table S2, Supporting Information), the methanediide ligand is best described as the structure A (Scheme 2). Scheme 2. Resonance Structure A of the Methanediide Ligand
Accordingly, the S(2) and S(3) atoms donate one of the lone pair electrons to the Sn(4) atom, while the N(1−3) atoms donate one of the lone pair electrons to the Sn(1−3) atoms, respectively. As a result, there are one LP (p orbital) remaining on the N(1−3) atoms, two LPs remaining on the S(2−3) atoms (S(2) sp0.43, p; S(3) sp0.44, p), and three LPs (sp0.28, p, sp16.73) remaining on the S(1) atom (Table S1, 3999
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Supporting Information). Thus, the theoretical studies are consistent with the X-ray crystallographic data of 2. In conclusion, reaction of [(PPh2NSiMe3)(PPh2S)CSn:]
Table 3. Crystallographic Data for Compound 2 2 formula M color cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V /Å3 Z dcalcd/g cm−3 μ/mm−1 F(000) cryst size/mm index range
(1) with elemental sulfur in toluene afforded [{(μ-S)SnIVC(PPh2NSiMe3)(PPh2S)}3SnII(μ3-S)] (2), which comprises a SnS moiety coordinated with a trimeric 2-stannathiomethanediide {(PPh2NSiMe3)(PPh2S)CSn(μ-S)}3. It was characterized by NMR spectroscopy, Mössbauer spectroscopy, X-ray crystallography, and theoretical studies. Conversion of compound 2 into SnS thin film or nanocrystal is currently under investigation.
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EXPERIMENTAL SECTION
All manipulations were carried out under an inert atmosphere of nitrogen gas using standard Schlenk techniques. Solvents were dried and distilled over Na/K alloy prior to use. 1 was prepared as described in the literature.4 The 1H, 13C, 31P, 119Sn, and 119Sn CPMAS NMR spectra were recorded on a JEOL ECA 400 spectrometer. NMR spectra were recorded in CD2Cl2. The chemical shifts δ are relative to SiMe4 for 1H and 13C and SnMe4 for 119Sn and H3PO4 for 31P. Elemental analyses were performed by the Division of Chemistry and Biological Chemistry, Nanyang Technological University. Melting points were measured in sealed glass tubes and not corrected. Synthesis of [{(μ-S)SnIVC(PPh2NSiMe3)(PPh2S)}3SnII(μ3-S)] (2). A solution of S8 (0.013 g, 0.05 mmol) in toluene (7 mL) was added dropwise to 1 (0.23 g, 0.19 mmol) in toluene (15 mL) at 0 °C. The yellow suspension was raised to room temperature and stirred for 4 h. The solution became red and clear. The resultant red solution was filtered and concentrated to afford 2 as orange crystals. Yield: 0.058 g (29.2%). Single crystals suitable for X-ray crystallography were obtained by recrystallization of compound 2 in C6D6. Mp. 186.7 °C. Anal. Calcd for C84H87N3P6S7Si3Sn4: C, 47.86; H, 4.16; N, 1.99. Found: C, 47.52; H, 4.03; N, 1.65. 1H NMR (399.5 Hz, 21.8 °C): δ = −0.29 (s, 27H, SiMe3), 6.88−7.38 ppm (m, 60 H, Ph). 13C{1H} NMR (100.5 MHz, 21.7 °C): δ = 2.74 (SiMe3), 128.45, 130.67, 130.85, 132.54−132.85 (m) ppm (Ph). 31P{1H} NMR (161.7 MHz, 21.9 °C): δ = 27.42 (d, 2JP−P’ = 8.67 Hz), 30.07 ppm (d, 2JP−P’ = 8.68 Hz). 119 Sn{1H} NMR (149.0 MHz, 21.8 °C): δ = −242.1 ppm (m). 119Sn CPMAS NMR (149.0 MHz, spinning speed = 9 kHz): δiso = −260.3 (Sn4), −232.3 ppm (Sn1−3). X-ray Data Collection and Structural Refinement. Intensity data for compound 2 were collected using a Bruker APEX II diffractometer. The crystal of 2 was measured at 103(2) K. The structure was solved by direct phase determination (SHELXS-97) and refined for all data by full-matrix least-squares methods on F2.16 All non-hydrogen atoms were subjected to anisotropic refinement. Hydrogen atoms were generated geometrically and allowed to ride in their respective parent atoms; they were assigned appropriate isotopic thermal parameters and included in the structure factor calculations. X-ray crystallographic data is summarized in Table 3. Mö ssbauer Spectroscopy. The air- and moisture-sensitive sample was received in a sealed ampule which was opened in an inert atmosphere glovebox and the powder transferred to an O-ringsealed Perspex sample holder which was immediately cooled to liquid nitrogen temperature. The sample was then transferred to the precooled cryostat and examined in transmission geometry using a BaSnO3 source at room temperature. Temperature control and monitoring was effected as described earlier,17 and all IS are referred to a BaSnO3 room-temperature reference spectrum. Spectrometer calibration was derived from an α-Fe absorption spectrum at room temperature.
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no. of reflns collected R1, wR2 (I > 2(σ)I) R1, wR2 (all data) goodness of fit., F2 no. of data/restraints/params. largest diff. peak, hole/e Å−3
C108H87D24N3P6S7Si3Sn4 2444.41 orange monoclinic P2(1)/c 16.4619(10) 33.693(2) 19.8683(12) 90 92.672(4) 90 11008.1(12) 4 1.475 1.196 4896 0.20 × 0.10 × 0.10 −21 ≤ h ≤ 21 −44 ≤ k ≤ 45 −25 ≤ l ≤ 26 147 130 0.0770, 0.1862 0.1327, 0.2238 1.176 27312/404/1235 1.860, −1.998
ASSOCIATED CONTENT
S Supporting Information *
Selected calculation results of 2; CIF file giving X-ray data of 2. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] (C.-W.S.);
[email protected] (R.H.H.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the Academic Research Fund Tier 1 (C.-W.S., RG 57/11; K.H.L., RG 28/07).
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REFERENCES
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